The labilization of hemoglobin by cobalt. Its effect on globin synthesis in reticulocytes

To elucidate a mechanism for cobalt-stimulated globin synthesis in rabbit reticulocytes, the cells were incubated with 1 mM CoCl2 containing 60Co. Although the cells incorporated cobalt irreversibly, evidence for the synthesis of cobalt-protoporphyrin was not obtained. More than 90% of the cobalt recovered in the cell cytoplasma was bound to the globin moiety of hemoglobin. Similar results were obtained with erythrocytes and purified hemoglobin incubated with 60CoCl2. By CM-Sephadex chromatography and isoelectric focusing it was found that cobalt-labelled hemoglobin differs slightly in charge from native hemoglobin, possessing a lower isoelectric point. It was also demonstrated that the heme in cobalt-labelled hemoglobin is less firmly bound to globin than the heme in the native protein, and that the purified cobalt-treated protein can stimulate globin synthesis in rabbit reticulocytes. It is postulated that in reticulocytes cobalt stimulates globin synthesis indirectly by labilizing intracellular hemoglobin.